Method for Alkaliating Anodes

ABSTRACT

The present invention relates to a method for lithiation of an intercalation-based anode or a non-reactive plating-capable foil or a reactive alloy capable anode, whereby utilization of said lithiated intercalation-based anode or a plating-capable foil or reactive alloy capable anode in a rechargeable battery or electrochemical cell results in an increased amount of lithium available for cycling, and an improved reversible capacity during charge and discharge.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/662,115, filed on Jun. 20, 2012 and U.S. Provisional Application No.61/565,580, filed on Dec. 1, 2011. The entire teachings of the aboveapplications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

In the field of rechargeable batteries or electrochemical cells wheremetal ions are shuttled between cathode and anode at varying voltages,the initial source of metal ions (usually alkali metal) is typically thecathode material. An example of said metal ions includes lithium.

During the initial cycling of a lithium ion rechargeable battery,passivation films are formed on the anode and cathode, but particularlyon the negative electrode. As shown in FIG. 1, several reactions cantake place as this film is formed on the negative electrode, includingsolvent reduction, salt reduction, insoluble product formation, andpolymerization. The passivation film is often referred to as an SEIlayer (solid electrolyte interphase), the formation of which results inthe loss of metal ions through an irreversible reaction, as well as asignificant loss in battery capacity. Most often, lithium ion batteriesare described as having an irreversible initial loss of 10 to 30%. Asecond type of irreversible loss of metal ions (e.g. lithium+) is due toside reactions that occur during the “shuttling” of metal ions duringeach additional charge and discharge cycle of the metal ion battery. Athird type of irreversible loss is represented by a cathode passivationlayer formation composed of soluble and insoluble lithium salts.

Precautions are taken to limit all types of irreversible losses (SEI,cathode passivation layer, and side reactions during long cycling). Itwould be advantageous, however, if a source could be provided tocompensate for the excess metal ion requirement, in an amount necessaryto support long cycle life. In most commercial metal ion batterysystems, this reserve is provided by the cathode, and therefore thecathode must necessarily be sized to be about 135 to 150% of thespecified discharge capacity of the battery, thus increasing the totalweight of the battery. Once the irreversible loss of metal ions relatedto SEI and cathode passivation layer formation is complete, up to 30% ofthe cathode's metal-donating material has become “dead weight”, ornon-operating material. Examples of these heavy and expensive cathodematerials are LiFePO₄, LiMn₂O₄ etc.

There have been attempts to source lithium metal to the anode during theconstruction of the anode. For example, FMC Corporation (Philadelphia,Pa.) has developed a stabilized lithium source called stabilized lithiummetal powder, or SLMP (U.S. Pat. No. 8,021,496). This material can bemixed into carbon before an activation step, such as crushing ordissolving by the electrolyte (U.S. Pat. No. 7,276,314). However, SLMPis a very expensive lithium source compared to even common cathodedonating materials, and may be difficult to distribute evenly.

Another example of sourcing metal to the anode is found in Li/polymerbatteries, where Li metal is placed on a current collector to form ananode containing all the required overcapacity. The coulombic efficiencyof this approach, however, is low when compared to the graphite anodebased gel or liquid electrolyte battery approach. Furthermore, while thespecific capacity is the highest possible, the cost of lithium metalfoil is fairly high and the discharge rates for the necessary solidpolymer electrolytes are low.

Others have attempted to increase the amount of alkali metal that isavailable during charge/discharge of an electrochemical cell using aprocess called pre-lithiation, first charging, or pre-charging, whereina passivation film is either chemically or electrochemically formed onthe anode prior to final assembly of the battery (U.S. Pat. No.5,595,837; U.S. Pat. No. 5,753,388; U.S. Pat. No. 5,759,715; U.S. Pat.No. 5,436,093; and U.S. Pat. No. 5,721,067). In the cases whereelectrochemical pre-lithiation was conducted, either alithium-containing electrode (most often consisting of elemental lithiummetal), or a lithium foil was employed as the source of lithium. Analternate process that circumvents the formation of a passivation film,and thus the need to use pre-lithiation, is disclosed in U.S. Pat. No.5,069,683.

SUMMARY OF THE INVENTION

The present invention relates to the discovery of an improved processfor lithiating (and/or alkaliating) anodes over known commercialprocesses. The novel processes overcome problems in the prior art byproviding a good electrochemical process that is roll to roll compatiblewith current assembly methods, can use inexpensive Li bearing salts withgood to excellent efficiency, particularly when used in combination withnon-aqueous solvents that do not react with the anode during lithiation.Preferred non-aqueous solvents dissolve and do not ionize the lithiumsalts, match the desired electrochemical window, or are substantiallyinert to the anode binder material. Preferred solvents possess a boilingpoint distant to that of water. A solvent or solvent condition thatwould meet all of the criteria including salt solubility, ionicconductivity, electrochemical window, and ease of water separation ispreferred.

Although several lithium bearing salts can be used in electrolysis, onlythe least expensive such as LiCl, LiBr, LiF, LiNO₃ for non-limitingexamples are preferred for low cost production. Until now, there hasbeen no process that would allow these types of salts to be used asfeedstock in the production of battery anodes. Until now, 30% efficiencywould have been the limit using non-aqueous solvents, making productiontoo costly. A satisfactory refinement process has not been found toproduce low moisture, pure solvent/salt solutions. Compounds formed byside reactions will eventually interfere with the formation of asuccessful SEI layer; only insoluble SEI material is desirable (usuallyformed in the complete battery cell), while these typical electrolysisbyproducts are not. Until now, a continuous refinement process has notbeen found, making it impractical to pre-lithiate battery orelectrochemical cell anodes using salt as a feedstock. For the purposeof eliminating the mentioned limitations and creating a low costpre-lithiated anode, a novel process is now disclosed.

For the purpose of this discussion, lithiation is the electrochemicalintroduction of lithium into and/or on a material (preferably an anode)and includes: electrochemically transporting ions of lithium into ananode material as in intercalation; electrochemically transportinglithium ions onto an anode current collector surface as in plating;electrochemically transporting lithium ions into an alloy of an anodemetal as in alloying; and/or electrochemically transporting lithium ionsinto a surface layer of the anode, e.g. an SEI layer. Plating refers toforming a layer of atoms onto the immediate surface of a substrate,usually a metal through an electrolytic process. Alloying refers to aplating process where lithium atoms wind up in a homogeneous mixturewithin the host substrate, such as with aluminum or tin. Intercalationrefers to a process where lithium ions are inserted between planes of ananode host material such as carbon or silicon. In some instances withinthe description, lithiation, intercalation, lithium plating or alloyingare used interchangeably. In each instance where lithiation with salt isdiscussed below, lithiation with a lithium halide salt is understood tobe preferred. Additionally, it is possible to use other alkali metalhalide salts or alkali metal salts in lieu of lithium salts to achievealkaliation in each of the processes described herein.

By lithiating the anode prior to battery assembly, a surplus of lithiumis present that can support longer cycling life, initial losses due toSEI formation, cathode related alkali metal ion losses, and/or alkalimetal free cathode material cycling needs. The lithiation method can beimplemented on a continuous or batch basis. In one embodiment, ametal-intercalating material, such as carbon, graphite, tin oxide, andsilicon, is coated onto a current collector of a conductive materialsuch as copper, coated aluminum or carbon fiber, forming theintercalation-based anode. A bath containing a non-aqueous solvent suchas, but not limited to gamma butyrolactone (GBL), and at least onedissolved lithium salt such as, but not limited to LiCl, contacts theanode. Other solvents can be used and preferably are selected toexhibit: adequate salt solubility; a suitable electrochemical window;good ionic conductivity; low temperature boiling point under high vacuumconditions (e.g. less than 130° C. at 1 mTorr) to reduce risk of solventdegradation; a differential boiling point from water (e.g. 25° C.minimum) to facilitate water separation; miscibility with other cyclicand linear solvents; and/or no propensity to attack typical anodebinders. Other lithium salts can be used, preferably ones that produceeasily managed byproducts, more preferably those that have gaseousbyproducts. Preferably the salt should also exhibit low solubility incommon linear solvents such as DMC so that the salt may be recovered andcleansed easily for reuse after lithiation. A sparging gas such as CO₂or SO₂ can be added to the lithiation bath in order to: increase thelithium salt solubility; increase the ionic conductivity; improve thequality of the SEI layer; and/or increase the lithiation efficiency ashas been discovered. Electrolytic field plates are provided. A reducingcurrent is applied to the anode in such a way as to lithiate. At thefield plate, there is an oxidizing current, so there is a need to use aninert material such as platinum, or carbon. In another preferredembodiment, the byproduct of the lithiation process is limited to anevolving gas at the counter electrode (field plate). The full complementof lithium ions is provided in this way. In another embodiment, alithium non-interactive current collector may be plated using thismethod. In another embodiment, an alloying metal foil or coating may belithiated in this method.

After lithiation, it may be desirable to reduce the amount of remainingsalt or lithiation solvent in the anode. An additional step comprising arinse with a solvent (such as GBL or DMC) but without the salt contentto reduce the remaining salt content in the lithiated anode can beperformed. Alternately a pair of rollers can be used to remove excesssurface fluids from the anode as it departs the lithiation tank.Alternately, the processed and rinsed anode can be vacuumed dried,thereby removing the remaining solvent, making it capable of long-termstorage and compatible with subsequent use in a normal battery assemblyprocess.

The invention provides a method for lithiation of an anode, preferably,in a continuous process, comprising the steps of:

(a) providing an anode;

(b) providing a bath comprising a non-aqueous solvent and at least onedissolved lithium salt, preferably a lithium halide salt, such aslithium chloride, wherein said bath contacts the anode, preferably in acontinuous process, and wherein a dry gas blankets said bath;

(c) providing an electrolytic field plate comprising an inert conductivematerial wherein said field plate establishes a field between the anodeand the field plate; and

(d) applying a reducing current to the anode and an oxidizing current tothe field plate, wherein metal ions from the bath lithiate the anode.

The invention also discloses a method for lithiating an anode in acontinuous process, wherein the lithiated anode provides for the reducedirreversible capacity for the whole cell or provides for the wholeamount of lithium necessary to operate a non lithium metal containingcathode material, comprising the steps of:

(a) providing an anode comprising a lithium active material, or aninactive substrate that can be plated;

(b) providing a bath comprising a non-aqueous solvent and at least onedissolved lithium halide salt, wherein said bath contacts the anode in acontinuous process, and wherein a dry gas blankets said non-aqueoussolvent and at least one dissolved lithium halide salt;

(c) providing an electrolytic field plate, comprising an inertconductive material wherein said field plate establishes a field betweenthe anode and the field plate;

(d) applying a reducing current to the anode, wherein metal ions willlithiate the anode in a continuous process;

(e) applying an oxidizing current to the field plate; and

(f) collecting an evolving gas or byproduct generated at the fieldplate.

In one embodiment, the anode material is selected from carbon, coke,graphite, tin, tin oxide, silicon, silicon oxide, aluminum,lithium-active metals, alloying metal materials, and mixtures thereof,wherein said anode material is coated onto a current collector of aconductive material selected from copper and carbon fiber.

In a further embodiment, the non-aqueous solvent is selected frombutylene carbonate, propylene carbonate, ethylene carbonate, vinylenecarbonate, vinyl ethylene carbonate, dimethyl carbonate, diethylcarbonate, dipropyl carbonate, methyl ethyl carbonate, acetonitrile,gamma-butyrolactone, room temperature ionic liquids, and mixturesthereof. In a preferred embodiment, the non-aqueous solvent isgamma-butyrolactone.

In another embodiment, the halide salt is that of Na or K. In anotherembodiment, the lithium containing salt is LiNO₃. In yet anotherembodiment, the lithium halide salt is selected from LiCl, LiBr, LiF,and mixtures thereof. In a preferred embodiment, the lithium halide saltis LiCl.

In yet another embodiment, the non-aqueous solvent contains an additivethat facilitates the formation of a high quality SEI layer. For example,VC, EC or maleic anhydride could be added to the non-aqueous solvent.

In yet another embodiment, a sparged gas such as CO₂ or SO₂ isincorporated into the lithiation bath in order to: increase the saltsolubility, increase the ionic conductivity, support good quality SEI inthe form of Li₂CO₃ or Li₂SO₃, and increase the efficiency of theintercalation. The sparged gas is bubbled to create up to atmosphericpressure saturation. Higher levels of saturation are also beneficial,but this level of gas saturation is sufficient to increase theefficiency of lithiation. CO₂ is preferred because of its lower cost andlower toxicity. Samples of graphite anodes were pre-lithiated to 1mAhr/cm² in the described method but with and without bath CO₂saturation. The resulting anodes were delithiated against a lithiummetal counter electrode in a quartz beaker to +1 volt above lithiummetal to determine the reversible lithium content. In all cases, thereversible lithium amount was greater in the CO₂ examples than thosewithout CO₂. FIG. 9 shows the improvement of the lithiation process whenCO₂ is sparged into the lithiation process tank. This represents asignificant improvement to any commercial application of pre-lithiation.

In each instance where lithium, lithium salts and/or lithiation arediscussed below/above, it is understood that other alkali metals andalkali salts can be used and alkaliation can be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: Characterization of the SEI layer on carbon negative electrode(anode).

FIG. 2: Lithiation tank layout.

FIG. 3: Lithiation system layout with a solvent conditioning system andsalt replenishment system.

FIG. 4: Multi-tank lithiation layout.

FIG. 5: First charge and discharge of a standard anode versus LiFePO4cathode.

FIG. 6: First charge and discharge of a pre-lithiated anode versusLiFePO4 cathode.

FIG. 7: Lithiation system layout with a solvent conditioning system,solvent distillation system, and salt replenishment system.

FIG. 8: Cell capacity comparison of LiCoO₂/graphite control versuspre-lithiated button cell.

FIG. 9: Lithium intercalation efficiency with CO₂ and without CO₂.

FIG. 10: Coulombic efficiency of pre-lithiated and control sample cells.

FIG. 11: Comparative heat test results of pre-lithiated and controlsample cells.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Anodes comprised of metal oxides or metal alloys or graphite or carbonor silicon or silicon/carbon blends, such as anodes comprised ofgraphite or carbon, are lithiated during the first charging step in thebattery operation after assembly, with lithium coming from the cathodematerial. In these cases, the cathode is the heaviest and most expensivecomponent in the battery. It would therefore be desirable and ofcommercial importance to reduce the weight of the cathode, with minimalloss to the battery efficiency and output. If the dead weight thatresults from SEI and cathode passivation layer formation could beeliminated by sourcing the metal ions in such a way that alleviated theeffects of the irreversible losses of the metal ions, then the specificcapacity and volumetric capacity density of the battery could beincreased, and cost of the battery could be reduced.

The present invention relates to a method for lithiation of anintercalation-based anode, a non-reactive plating-capable foil, or analloying capable film or foil whereby utilization of said lithiatedanode in a rechargeable battery or electrochemical cell results in anincreased amount of lithium available for cycling, and an improvedreversible capacity during charge and discharge. The additional lithiumavailable may also support the cycling of an initiallynon-lithium-containing cathode material. As mentioned above, anodescomprised of graphite or carbon or silicon or silicon-carbon blends havebeen lithiated during the first charging step in the battery operationafter assembly, with lithium coming from the cathode material. In thesecases, the cathode is the heaviest and most expensive component in thebattery. One of the desired features in lithium battery technology is toreduce the weight of the battery coming from the excess cathodematerial, without compromising battery efficiency and output.

A method for fabricating a lithiated anode which provides increasedamounts of lithium available for cycling, improved reversible capacityduring charge and discharge of a rechargeable battery and a consequentlighter battery is disclosed in FIG. 2. Electrolytic field plates areheld at a voltage necessary to establish a field between the anode andthe field plate, and to lithiate the anode, such as to plate orintercalate lithium onto a foil, or into an anode substrate or sheet, orto form an SEI layer upon the anode. A typical operating voltage forthis is 4.1V. An appropriate reference electrode, such as Ag/AgNO₃non-aqueous reference from Bioanalytical Systems, Inc., located close tothe targeted negative electrode may be preferred to monitor the anodeconditions. It is possible to operate the field plates in either voltageor current control mode. With current control, the full operatingpotential may not be immediately obtained. This operation under currentcontrol may result in lower initial operating voltages. This lowervoltage may prefer secondary side reactions instead of the dissociationof the lithium halide salt (e.g. LiCl) and the resulting intercalationof the anode material. Operating under voltage control can ensure thatthe field plate potential is immediately set to a sufficient potentialto favor the dissociation of the lithium halide salt (e.g. 4.1 Volt forLiCl) and to minimize secondary side reactions. Current control canalternatively be used if the subsequent operating voltage remains abovethe lithium halide salt dissociation threshold. This can be done bysetting a sufficiently high initial current density (e.g. 2 mA/cm²) thatwill favor the dissociation rather than secondary side reactions. Anoxidizing current is applied at the field plate, so there is a need touse an inert material or a conductive oxide. In one embodiment, theinert material comprising the field plate is selected from glassycarbon, tantalum, gold, platinum, silver, and rhodium. In a preferredembodiment, the inert material comprising the field plate is selectedfrom platinum, gold or carbon. In a more preferred embodiment, the inertmaterial comprising the field plate is carbon or glassy carbon. Thefield plates may also be comprised of a base material such as stainlesssteel that is plated with an inert conductive material such as gold,platinum, or glassy carbon. The field plates are immersed within thebath, with the anode passing between the field plates as illustrated inFIGS. 2 and 4. The field plates can be operated as a single entity at asingle controlled voltage or current density, or multiple plates can beimplemented that allow for independent control of voltage or currentdensity over multiple zones. This is illustrated in FIGS. 2 and 4.

The anode typically comprises a compatible anodic material which is anymaterial which functions as an anode in an electrolytic cell. As hereindisclosed, the term anode is equivalent to the terms negative electrode,conductive foil, anode sheet, anode substrate, or non-reactiveplating-capable foil. In one embodiment, anodes arelithium-intercalating anodes. Examples of materials that compriselithium-intercalating anodes include but are not limited to carbon,graphite, tin oxide, silicon, silicon oxide, polyvinylidene difluoride(PVDF) binder, and mixtures thereof. In a further embodiment,lithium-intercalating anode materials are selected from graphite, cokes,mesocarbons, carbon nanowires, carbon fibers, silicon nanoparticles orother metal nanomaterials and mixtures thereof. In another embodiment,alloying metals such as tin or aluminum may be used to host the lithiummetal as a result of the lithiation. A reducing current is applied tothe anode in such a way as to intercalate the lithium. The anode isbathed in a solution comprising a non-aqueous solvent and at least onedissolved lithium salt. The term non-aqueous solvent is a low molecularweight organic solvent added to an electrolyte which serves the purposeof solvating the inorganic ion salt. Typical examples of a non-aqueoussolvents are butylene carbonate, propylene carbonate, ethylenecarbonate, vinylene carbonate, vinyl ethylene carbonate, dimethylcarbonate, diethyl carbonate, dipropyl carbonate, methyl ethylcarbonate, acetonitrile, gamma-butyrolactone, triglyme, tetraglyme,dimethylsulfoxide, dioxolane, sulfolane, room temperature ionic liquids(RTIL) and mixtures thereof. In one embodiment, a non-aqueous solvent isselected from ethylene carbonate, vinylene carbonate, vinyl ethylenecarbonate, gamma-butyrolactone, and mixtures thereof. In a secondembodiment, a non-aqueous solvent is gamma-butyrolactone. In a thirdembodiment, an additive can be introduced to support high quality SEIformation. The additive could be vinylene carbonate, ethylene carbonateor maleic anhydride. In a fourth embodiment, a gas such as CO₂ or SO₂ issparged into the non-aqueous solution in order to: increase saltsolubility; increase the ionic conductivity; support the formation of anLi₂CO₃ or Li₂SO₃ SEI layer; and increase the lithiation efficiency. FIG.9 describes the efficiency of reversible lithium intercalation from aninitial amount of lithium sourcing measured in mAhr. The lost amount canbe described as side reactions such as but not limited to SEI formation.

The term alkali metal salt refers to an inorganic salt which is suitablefor use in a non-aqueous solvent. Examples of suitable alkali metalcations comprising an alkali metal salt are those selected from Li⁺,Na⁺, K⁺, Rb⁺, Cs⁺, Fr⁺, and mixtures thereof. Examples of suitablehalogen anions comprising an alkali metal salt are those selected fromF, Cl⁻, Br⁻, I⁻, and mixtures thereof. In one embodiment, the alkalimetal salt is selected from LiF, LiCl, LiBr, NaF, NaCl, NaBr, KF, KCl,KBr, and mixtures thereof. Other salts such as LiNO₃ may be used, but inthe preferred embodiment, the alkali metal salt is the halide LiCl.

Inexpensive salts with gaseous decomposition products can be halidessuch as LiCl, LiBr, and LiF. LiCl and other simple salts can bedifficult to dissolve or ionize in non-aqueous solvents. Solvents suchas propylene carbonate (PC), dimethyl carbonate (DMC), and acetonitrilesupport only trace amounts of LiCl in solution without the use of acomplexing agent such as AlCl₃. AlCl₃ and other complexing agents can bedifficult to handle in regard to moisture management and highcorrosivity. In addition, some solvents that can dissolve halide salts,such DMSO or tetrahydrofuran (THF), do not allow complete ionization ofthe salt, and/or attack the binding polymers in the anode composites.Gamma-butyrolactone has been found to facilitate the dissolution andionization of the desirable alkali metal halide salts. It combines goodsolubility of the alkali metal halide salts with compatibility with TFETeflon_(c), PVDF, butadiene rubber and other binders. The use of halidesalts with gaseous decomposition products such as LiCl prevents theproduction of solid precipitates during the lithiation process. Sincethe lithiation process products are primarily lithium ions and gas,there are few solid precipitates or intermediate compounds that canaccumulate in the non-aqueous solvent solution. Removal of dissolved gasfrom the non-aqueous solvent solution is preferred over solidprecipitates during long term continuous operation of a productionsystem.

Gamma-butyrolactone also has a capable electrochemical window, includingthe lithium potential near −3 volts vs. a standard hydrogen electrode(SHE). It is a capable electrolyte with high permittivity and lowfreezing point, and can dissolve and ionize up to a 1 M concentration ofLiCl. A modest amount of heat can be used to reach this value. In oneembodiment, the heat to dissolve and ionize up to a 1 M concentration ofLiCl is between about 30° C. and 65° C. In a more preferred embodiment,the heat is between about 38° C. and 55° C. In a most preferredembodiment, the heat is about 45° C. The lithiation tank can also havean internal circulating pump and distribution manifold to preventlocalized salt concentration deprivation.

It has been discovered here that a dissolved gas such as CO₂ or SO₂ canenhance the lithiation process. It increases the solubility of the salt,the ionic conductivity of the non-aqueous solvent, and doubles theefficiency of lithiation. Since CO₂ is inexpensive, easily dried,chemically safe, and a potential building block gas for a high qualitySEI layer, it has been selected as the preferred dissolved gas. CO₂preferentially reacts with trace H₂O and Li⁺ during the lithiationprocess to form a stable, insoluble SEI material (Li₂O, Li₂CO₃ etc.).FIGS. 8 and 10 exemplify the operating efficiency of the LiCoO₂/graphitecells with and without pre-lithiation. The moisture level in thelithiation tank is driven down by the consumption of CO₂ and H₂Oaccording to this process, and care is given to control the moisturelevel in the tank to between about 5 to 20 ppm (see FIG. 2). In thisway, anode lithiation with a quality SEI material is producedcontinuously.

The intercalation or plating process for lithium ions (or generallylithiation) from 1 M LiCl salt in gamma-butyrolactone solvent will occurat about 4.1 volts measured between the anode sheet and the referenceelectrode up to a reducing current density of 2 mA/cm² or more. Asintercalation rates are increased too far beyond this current density,dendrites or lithium plating may begin to take place which harm thefinal battery or electrochemical cell performance. This will varydepending on the graphite porosity etc. In order to control both thecurrents and dependant voltages accurately, it may be necessary todivide the field plate into zones as shown in the FIGS. 2 and 4. Othermetals can also be plated or intercalated with this method includingsodium as an example. As mentioned above, the byproduct of theintercalation process when using a halide alkali metal salt is anevolving gas at the counter electrode (field plate). In a preferredembodiment, the evolving gas is selected from F₂, Cl₂, Br₂, and mixturesthereof. In a more preferred embodiment, the evolving gas is Cl₂.

Prior to entering the lithiation bath, the anode material can bepre-soaked in an electrolyte solution as shown in FIG. 4. Thepre-soaking of the anode material will ensure full wetting of thematerial prior to the start of the lithiation process. This pre-soakbath can contain a non-aqueous solvent with or without a lithium salt,with or without a sparge gas, and with or without an SEI promotingadditive.

The evolution of gas at the field plate or counter electrode can resultin evolving gas entering into, and/or being released from, the bathsolution. As a result, controlling the build-up of dissolved andreleased gas is desired to avoid corrosion, as for example, in thehypothetical case of trace water contamination reacting with chlorinegas, to form HCl during chlorine gas evolution. The tank assembly can beconfigured to control the introduction of moisture into the system byusing a dry gas blanket on top of the liquid. In one embodiment, the drygas (1-10 ppm moisture) is selected from helium (He), neon (Ne), argon(Ar), krypton (Kr), xenon (Xe), sulfur hexafluoride (SF₆), nitrogen(N₂), dry air, carbon dioxide (CO₂) and mixtures thereof. In a preferredembodiment, the dry gas is selected from nitrogen, argon, carbondioxide, dry air and mixtures thereof. Moisture ingress can also becontrolled by having a long narrow gap entry and exit tunnel for theanode film where a counter flowing dry gas is used to mitigate air entryinto the system.

FIGS. 2, 3, 4 and 7 illustrate a process and apparatus that continuouslycontrols moisture, gas, and small quantities of lithiated organiccompounds during a continuous lithiation process. Liquid is drawn from abath through a series of valves. The liquid can be delivered in a batchmode to a refluxing unit, or it can be continuously circulated through aconditioning loop including distillation or reverse osmosis. The refluxunit can take batches of material through a vacuum refluxing processthat will remove both accumulated gas as well as moisture from theliquid. In one embodiment, the accumulated gas is selected from F₂, Cl₂,Br₂, and mixtures thereof. In a more preferred embodiment, theaccumulated gas is Cl₂. The use of reflux conditioning instead of adistillation process can prevent a change in the salt concentration ofthe working fluid which would result in a loss of salt content throughprecipitation. Once the batch liquid has been refluxed for a designatedperiod of time, the liquid can be returned to the bath with a lowermoisture and gas content. The size and rate of the reflux unit can bematched to the moisture ingress rate and to the gas production rate inorder keep the bath liquid at optimum conditions. The reflux rate can beincreased through use of multiple simultaneous batches and through theuse of high rate reflux equipment such as a rotary evaporator and highvacuum conditions. The reflux batch moisture content typically decays inan exponential fashion and the turnover rate can be tuned for optimalmoisture control with minimal energy input and equipment cost.

The refluxing unit can be placed after a salt dosing unit. The saltdosing unit can be used to add and mix the desired salt into thenon-aqueous solvent solution. The temperature of the dosing unit can beheld to maximize the solubility of the salt in the electrolyte and theelevated temperature can also be used as a pre-heating step for therefluxing unit. In one embodiment, the dosing unit maintains an elevatedprocess temperature of between about 30° C. and 65° C. In a morepreferred embodiment, the dosing unit maintains an elevated processtemperature of between about 38° C. and 55° C. In a most preferredembodiment, the dosing unit maintains an elevated process temperature ofabout 45° C. The benefit of dosing in the salt in a dosing unit beforethe refluxing unit is that the salt does not have to be in a completelydry state. Removing the moisture from a solid phase salt can be verydifficult. Once a salt is dissolved into solution, however, the watercontent of the salt can be removed through the refluxing process.Maintaining the dosing unit at an elevated temperature increases thesolubility of the lithium salt in the non-aqueous solvent and ensuresfull dissolution of the salt prior to the refluxing unit.

The conditioning/replenishment loop operates in a continuous mode andcan also be used to remove dissolved gases from the bath liquid throughuse of a membrane contactor. The gas output from the membrane contactorand the reflux unit can be passed through a scrubber to capture anyeffluent, such as chlorine gas, produced by the process. In oneembodiment, the dissolved gases are selected from F₂, Cl₂, Br₂, andmixtures thereof. In a more preferred embodiment, the dissolved gas isCl₂. The bath liquid can also be paired against either vacuum or a drygas within the membrane contactor in order to remove unwanted gases. Inone embodiment, the dry gas is selected from helium (He), neon (Ne),argon (Ar), krypton (Kr), xenon (Xe), sulfur hexafluoride (SF₆) nitrogen(N₂), carbon dioxide (CO₂), dry air and mixtures thereof. In a preferredembodiment, the dry gas is selected from nitrogen, argon, carbondioxide, dry air and mixtures thereof.

An inline heater can be used to maintain an elevated tank temperature tomaintain consistent bath operating conditions, even with variations infacility temperature. Elevated lithiation tank temperatures can aid inthe formation of a high quality SEI layer. In one embodiment, the inlineheater maintains an elevated tank temperature of between about 30° C.and 55° C. In a more preferred embodiment, the inline heater maintainsan elevated tank temperature of between about 30° C. and 45° C. In amost preferred embodiment, the inline heater maintains an elevated tanktemperature of about 40° C.

A filter unit can be used to remove any accumulated particulatecontamination. The filter unit can be located at various points in theloop including prior to the pump and after the salt dosing unit. Thefilter unit can be used to remove particulates from the non-aqueoussolvent in cases where a non-halide lithium salt such as LiNO₃ is usedsuch that a precipitate is formed at the field plates.

Lithium halide salt can be added to the non-aqueous solvent using thesalt dosing unit. An excess of solid lithium salt can be maintainedwithin the dosing unit to keep the lithium salt concentration within theloop and within the bath at the desired level (i.e., a saturatedsolution of about 0.5 M to 1.0 M) over long periods of time. The dosingunit can be configured to keep the solid salt from entering the bath orrefluxing unit. By dosing salt prior to the refluxing unit, there is noneed to separately dry the salt with its high water binding energy inits granular state. In one embodiment, the lithium salt within the saltdosing unit is selected from LiF, LiCl, LiBr, and mixtures thereof. In apreferred embodiment, the lithium halide salt within the salt dosingunit is LiCl. Dissolved lithium salts can be carried through the rest ofthe loop. The fluid circulation loop pump rate can be matched tomaintain a constant lithium salt concentration in the tank. For a givenanode substrate process rate, a matching loop circulation rate will dosethe same amount of lithium salt as the lithiation process consumes. Asthe anode process rate is increased or decreased, the loop circulationrate can be modified to maintain an equilibrium state within the bath.

Depending on the specific tank conditions, the bath fluid can be treatedusing a circulating loop, a refluxing unit or a distillation unit asshown in FIGS. 2 and 4. A circulating loop can dose in salt, removedissolved gases, control the bath temperature and removed particulatecontaminants. A refluxing unit is effective at removing dissolved gasesand for removing moisture content without reducing the salt content ofthe solution. A distillation unit is effective at removing dissolvedgases, removing moisture content, removing all salt content and removinglithiated organic compounds. The output from the distillation unit canbe fed back into a dosing and refluxing unit to reestablish the saltcontent if required. The effluent from the distillation unit can becollected and treated to recover used salt for reuse in the lithiationprocess. For example, DMC solvent will rinse away all but the insolublesalt so that the salt may be re-introduced into the dosing unit.Recirculating loops, refluxing unit and distillation units can be sharedacross multiple tanks that have different input and output requirementsas a means of minimizing equipment size and cost.

When the anode is lithiated to the extent of the irreversible andextended cyclic loss amount, it can be assembled into a rechargeablebattery or electrochemical cell with a smaller amount of lithium-bearingcathode material than would otherwise be required, thereby improving thespecific capacity, specific energy, volumetric capacity density andvolumetric energy density of the cell while reducing its cost.

When the anode is lithiated to the extent of the irreversible andextended cyclic loss amount, as well as the intended cycling amount, itcan be assembled into a battery or electrochemical cell with a cathodematerial that does not initially contain lithium. This type of cathodematerial can be much less expensive than lithium containing cathodematerials, and examples include, but are not limited to, MnO₂, V₂O₅ andpolyaniline. The cost of the battery or cell produced with this methodwill be lower due to the lower cost of the feedstock lithium salt.

Therefore, previous limitations to the low cost production of moreefficient lithium ion batteries and electrochemical cells are overcomeby the novel processes described here. The materials and processes ofthe present invention will be better understood in connection with thefollowing examples, which are intended as an illustration only and notlimiting of the scope of the invention.

EXAMPLES

The following is a detailed example of an anode preparation andprocessing. 25 micron thick copper foil was cleaned with isopropylalcohol and Kimberly-Clark Kimwipes to remove oil and debris and thendried in air. A solution was prepared by adding 2.1 grams of 1,000,000weight PVDF powder from Arkema Fluoropolymers Div. to 95 ml of dry NMPsolvent from Aldrich Chemical. The solution was mixed with a stir barovernight to fully dissolve the PVDF material. The solution was kept inthe dark to prevent the light sensitive solvent from reacting. 33.9 mlof this PVDF solution was then added to 15 grams of Conoco PhilipsCPreme G5 graphite and 0.33 grams of acetylene black and stirred for 2hours in a ball mill at 600 RPM without any mixing balls. The resultingslurry was cast onto the copper foil using a vacuum hold down plate withheating capability. The finished graphite thickness after casting anddrying at 120° C. was about 100 microns or 14 mg/cm₂. The anode sheetwas then die punched into 15 mm diameter discs and then pressed at about3000 psi and 120° C. for use in a 2032 button cell assembly. Thecopper/graphite anode discs were then vacuum baked at 125° C. and about1 mTorr in a National Appliance Company model 5851 vacuum oven for atleast 12 hours.

The anode discs were then transferred into a Terra Universal dry airglove box with −65° C. dew point air supplied by compressed dry airpassed through a Kaeser two stage regenerative drier. The anode discswere then vacuum infiltrated with a GBL solvent with a 0.5 Mconcentration of LiCl salt solution. This electrolyte solution had beenprepared by heating to 90° C. and then vacuum refluxing at about 1 mTorrfor 6 hours to remove moisture down to about 10 ppm. The anode discswere allowed to soak for a half hour at vacuum conditions, a half hourin atmospheric pressure conditions and a half hour in the lithiationvessel itself prior to any currents being passed. The lithiation vesselincluded a constant bubbling of CO₂ gas to achieve a saturation leveland a temperature of 30° C. Test leads from a Maccor 4300 battery testerwere connected to the anode sample (red working) and glassy carbon(black counter) electrode. Voltage at the working electrode is monitoredvia a Ag/AgNO₃ non-aqueous electrode. A reducing current of 2 mA/cm² wasapplied to the graphite anode until a total of 1 mAhr/cm² was achieved.The pre-lithiated anode disc was then rinsed in pure distilled GBL andvacuum dried. The anode discs were then assembled against either LiFePO₄or LiCoO2 12 mm diameter cathode discs. The separator used was Celguard2400, and about 0.2 ml of electrolyte was used in the assembly. Theelectrolyte was 1:1:1 EC:DMC:DEC with 1M LiPF₆ salt and 1% VC withmoisture levels at about 10 ppm. A vacuum was applied to the assembledcell to remove bubbles before crimping in an MTI model MT-160D crimpingtool. Subsequent electrical tests were then performed on the batterytester unit using a 12 hour delay, two about C/12 formation cycles to atleast 3.7 volts, about C/3 charge/discharge cycles, and 20 minute reststeps between them. All the battery tests were carried out in ahome-made environmental chamber controlled to 26° C.

A Maccor model 4300 battery tester was used to test the CR2032 sizebutton cells assembled with a CPreme graphite anodes, LiFePO₄ or LiCoO₂cathodes, and Celguard 2400 separators. Electrolyte solutions containinga 1:1:1 mixture of EC:DMC:DEC with 1 molar concentration of LiPF6 saltand 1% VC were used. Both anodes and cathodes were cast with PVDFbinders. First charge and discharge cycles, often called the formationcycles, were performed at a current rate of approximately C/12. FIGS. 5and 6 illustrate the first cycle irreversible loss using pre-lithiatedand non-pre-lithiated graphite anodes mounted against LiFePO₄ cathodes.The initial absolute charge capacity of the two samples is different dueto extraneous packaging variation. The irreversible losses arerepresentative of the methods described, however. In FIG. 5, thereversible capacity of the button cell is 56%. In FIG. 6, the reversiblecapacity of the button cell when matched to a pre-lithiated anode is98%. FIG. 8 shows a typical LiCoO₂/graphite vs. a LiCoO₂/pre-lithiatedgraphite, but otherwise identical sample, tested over an extended rangeof charges and discharge cycles at approximately a C/3 rate. The resultsindicate that there is a long lasting benefit to the battery cell due topre-lithiation using the methods described. FIG. 11 shows theeffectiveness of the SEI layer formed during the prelithiation process,by comparing capacity retention of the cell with prelithiated anode to acontrol cell, with both cells being subjected to 48 hours of 50° C. heatas a form of accelerated aging test.

An example of a salt other than LiCl that has been used by the inventorto achieve lithiation is LiNO₃. Reasonable rates of lithiation have beenachieved with LiNO₃. When the anodes pre-lithiated using LiNO₃ werepaired with LiFePO₄ cathodes, however, poor cycling resulted, possiblydue to an unidentified byproduct. This problem can be solved by aslightly more complicated removal process such as an additional anoderinse.

While there has been illustrated and described what is at presentconsidered to be the preferred embodiment of the present invention, itwill be understood by those skilled in the art that various changes andmodifications may be made and equivalents may be substituted forelements thereof without departing from the true scope of the invention.Therefore, it is intended that this invention not be limited to theparticular embodiment disclosed, but that the invention will include allembodiments falling within the scope of the appended claims.

What is claimed is:
 1. A method for lithiation of an anode, preferably,in a continuous process, comprising the steps of: (a) providing ananode; (b) providing a bath comprising a non-aqueous solvent and atleast one dissolved lithium halide salt, wherein said bath contacts theanode, preferably in a continuous process, and wherein a dry gas blanketcovers said bath; (c) providing an electrolytic field plate comprisingan inert conductive material wherein said field plate establishes afield between the anode and the field plate; and (d) applying a reducingcurrent to the anode and an oxidizing current to the field plate,wherein lithium ions from the bath lithiate into the anode.
 2. Themethod of claim 1, wherein the anode active material is selected fromcarbon, coke, graphite, tin, tin oxide, silicon, silicon oxide,aluminum, lithium-active metals, alloying metal materials, and mixturesthereof.
 3. The method of claim 1, wherein the non-aqueous solvent isselected from butylene carbonate, propylene carbonate vinylenecarbonate, vinyl ethylene carbonate, dimethyl carbonate, diethylcarbonate, dipropyl carbonate, methyl ethyl carbonate, acetonitrile,gamma-butyrolactone, room temperature ionic liquids, and mixturesthereof.
 4. The method of claim 3, wherein the non-aqueous solvent isgamma-butyrolactone.
 5. The method of claim 1, wherein the halogen ofthe dissolved lithium halide salt is selected from ionic F⁻, Cl⁻, Br⁻,I⁻ and mixtures thereof.
 6. The method of claim 1, wherein the dissolvedlithium halide salt is LiCl.
 7. The method of claim 1, wherein thedissolved lithium halide salt is LiBr.
 8. The method of claim 1, whereinthe dissolved lithium halide salt is LiF.
 9. The method of claim 1,wherein the electrolytic field plate is selected from platinum, gold,glassy carbon, and graphite.
 10. The method of claim 1, wherein thelithiated anode and foil are used in the final assembly of arechargeable battery.
 11. The method of claim 1, wherein the lithiatedanode is used in the assembly of an electrochemical cell to provide thelithium needed for cycling when paired with a cathode not initiallycontaining lithium.
 12. The method of claim 1, comprising the step ofperforming a pre-charging cycle upon the anode externally prior to theassembly of an electrochemical cell.
 13. The method of claim 1, whereinthe evolving gas generated at the field plate is captured by a refluxunit, a membrane contactor, a gas scrubber, and combinations thereof.14. The method of claim 1, comprising one or more reflux units, membranecontactors, gas scrubbers, baths, inline heaters, filters, salt dosingunits, pumps, valves, and combinations thereof, connected in a loopcomprising series and parallel connections.
 15. The method of claim 14,wherein said inline heaters heat a non-aqueous solvent and dissolvedalkali metal halide salt to a temperature of between 30° C. and 65° C.16. The method of claim 15, wherein said temperature is about 40° C. 17.The method as in claim 1, wherein a separate immersion bath is used torinse the anode in a solvent.
 18. A method as in claim 1, wherein thesalt is recovered periodically by distillation of the used non-aqueoussolvent and subsequent rinsing of the salt in a light non-solvatingfluid.
 19. The method of claim 1 or 14, wherein the rate of saidcontinuous process can be increased and decreased.
 20. The method ofclaim 1 or 17, wherein the rate of continuous lithiation of the anodeand foil can be increased and decreased.
 21. The method of claim 1 or17, wherein the rate of loop circulation can be increased and decreased.22. The method of claim 3, wherein the non-aqueous solvent contains anadditive to facilitate high quality SEI formation.
 23. The method ofclaim 22, wherein the additive is vinylene carbonate.
 24. The method ofclaim 1, wherein a dissolved gas is added.
 25. The method of claim 24,in which the dissolved gas is carbon dioxide.
 26. A method foralkaliation of an anode, preferably, in a continuous process, comprisingthe steps of: (a) providing an anode; (b) providing a bath comprising anon-aqueous solvent and at least one dissolved alkali metal salt,wherein said bath contacts the anode, preferably in a continuousprocess, and wherein a dry gas blanket covers said bath; (c) providingan electrolytic field plate comprising an inert conductive materialwherein said field plate establishes a field between the anode and thefield plate; and (d) applying a reducing current to the anode and anoxidizing current to the field plate, wherein metal ions from the bathalkaliate into the anode.